1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device having a gate electrode which comprises a SiGe layer.
2. Description of the Related Art
In manufacturing a semiconductor device, patterning of a conductive film or an insulating film is carried out by either forming a resist film on the conductive film or the insulating film which is formed on a semiconductor substrate and thereafter forming a resist pattern by photolithography or forming a hard mask pattern of SiO2 or the like thereon, and then applying etching to the conductive film or the insulating film with the pattern being used as a mask. For forming a minute pattern, dry etching is normally employed there at. However, when patterning by dry etching, contaminants such as dry etching products and particles are stuck onto the semiconductor substrate. If contaminants of this sort remain stuck thereon in the subsequent steps, decrease in production yield, deterioration of device characteristics and lower reliability may occur. Therefore, cleaning the semiconductor substrate after patterning is required so as to thoroughly remove the contaminants stuck onto the substrate.
In regards to the cleaning performed after patterning the insulating film, there is disclosed, for instance, in Japanese Patent Application Laid-open No. 142741/1992, an apparatus for manufacturing a semiconductor wherein a semiconductor wafer is treated with a cleaning solution. This publication describes that, after using a hydrofluoric acid based agent (a mixed solution of hydrofluoric acid and ammonium fluoride) for the treatment, a silicon oxide film overlying a silicon semiconductor wafer is patterned by means of wet etching. Then the substrate is treated with a mixed solution of sulfuric acid and hydrogen peroxide to remove the photoresist, and the wafer is cleaned with a mixed solution of ammonia, hydrogen peroxide and pure water to remove particles stuck on the wafer surface. Further, the publication mentions that drying the wafer tends to make particles strongly stuck to the wafer surface, and their removal is considerably difficult, and such a problem can be overcome if the treatment for the removal of the photoresist as well as that for the removal of particles are performed consecutively after wet etching of the silicon oxide film. Further, the publication indicates the apparatus for etching treatment of the silicon oxide film can also be used as an apparatus for etching treatment of the polysilicon film.
Meanwhile, with respect to the cleaning performed after patterning the conductive film, there is disclosed, for instance, in Japanese Patent Application Laid-open No. 223464/2000, that after a layered film made of a refractory metal film (WSi film) and a polycrystalline silicon film is laid on a semiconductor substrate, the layered film is patterned by means of dry etching to form a gate electrode. The substrate is then cleaned with a mixed solution of ammonia and hydrogen peroxide at 35xc2x0 C. or 45xc2x0 C. to remove etching residues deposited on the substrate.
In Japanese Patent Application Laid-open No. 223464/2000, it is also mentioned that, if cleaning of the substrate with a mixed solution of ammonia and hydrogen peroxide lasts for a long time period, the lateral faces of the WSi film which constitutes the gate electrode may be excessively dissolved, creating a eroded film section. For the purpose of achieving both the prevention of such a film erosion of the WSi film and the substantially thorough removal of the deposit like dry etching residues, this publication proposes that the cleaning of the substrate is performed only for a specific time period, which is predetermined using the dummy substrate. Further, in the publication, it is described that a contact hole is formed by dry etching in an interlayer insulating film made of a plurality of insulating films (a silicon oxide film, a BPSG (Boro-Phospho-Silicate Glass) film, a BSG (Boro-Silicate Glass) film) which have different etching rates for the wet etching treatment, and that etching residues stuck on the surface of this contact hole are removed by cleaning with a mixed solution of ammonia and hydrogen peroxide. Also in this cleaning, if the treatment time period is set too long, the internal wall of the contact hole becomes uneven due to the differences in the etching rate so that, for the purpose of achieving both prevention of creation of such unevenness and removal of etching residues, this publication proposes that the cleaning is performed only for a specific time period, which is predetermined using the dummy substrate.
In recent years, viewed from the point of improving electrical characteristics of the device, the semiconductor device having a gate electrode which comprises a SiGe layer and a polycrystalline silicon layer has been put forward. For example, a semiconductor device having a gate electrode, wherein a lower layer is a SiGe (poly-Si0.8Ge0.2) layer for controlling the work function, and an upper layer is a polycrystalline silicon (poly-Si) layer was proposed and its device characteristics were also described in detail (Y. V. Ponomarev et al., IEDM"" 97, p.829).
Further, a semiconductor device having a gate electrode comprising a SiGe (poly-Si1xe2x88x92xGex) layer which is doped with P or B was reported (Wen-Chin Lee et al., 1998 Symposium on VLSI Technology Digest of Technical Papers, p. 190). There was also described a semiconductor device having a gate electrode (Ni(SixGe1xe2x88x92x)/poly-Si0.8Ge0.2) which is formed by growing Ni/TiN on a SiGe (poly-Si0.8Ge0.2) layer and applying the annealing thereto (Ja-Hum Ku et al., 2000 Symposium on VLSI Technology Digest of Technical Papers, p. 114).
A gate electrode pattern made of a SiGe layer and a polycrystalline silicon layer is formed by applying layers of an oxide film, a SiGe film and a polycrystalline silicon film, in this order, over a semiconductor substrate and forming a resist film on this layered film, and thereafter forming a resist pattern by photolithography and then dry etching the layered film with this resist pattern being used as a mask. However, after patterning is made by dry etching in this way and thereby a gate electrode pattern as well as a gate oxide film pattern are formed, dry etching products formed by the chemical reaction between the etching gas and the objects for etching and particles are left stuck onto the semiconductor substrate surface and the gate electrode. Therefore, it is required to clean the semiconductor substrate so as to remove such contaminants.
Yet, for removing dry etching products and particles which are stuck onto the semiconductor substrate and the gate electrode, if cleaning is carried out by the conventional cleaning method using a mixed solution of ammonia and hydrogen peroxide, there may arise a problem of film erosion of the lateral faces (referred to as xe2x80x9cside etchxe2x80x9d, hereinafter) of the SiGe layer.
Referring to FIG. 2, the above problem of the conventional cleaning method is further described below. FIG. 2(a) is a schematic cross-sectional view of a semiconductor substrate after formation of a gate electrode pattern and a gate oxide film pattern but before cleaning, and FIG. 2(b) is a schematic cross-sectional view of a semiconductor substrate after cleaning. In the drawings, referential numeral 1 represents a semiconductor substrate; 2, a gate oxide film; 3, a SiGe layer; 4, a polycrystalline silicon film and 5, an element isolation region.
As described above, when a layered film comprising a SiGe film is dry etched, using a resist pattern as a mask (FIG. 2(a)), dry etching products and particles (not shown in the drawings) are stuck onto the semiconductor substrate surface and the gate electrode. In order to remove the dry etching products and the particles which are stuck onto the semiconductor substrate, a mixed solution of ammonia and hydrogen peroxide used in the conventional cleaning method may be still employed. But, to achieve satisfactory removal of dry etching products, the ammonia concentration and the temperature of the mixed solution must high. The reason for the high ammonia concentration is that the dry etching products originating from the SiGe layer has difficulty dissolving into this mixed solution.
However, when cleaning is performed using the mixed solution with a high ammonia concentration at a high temperature so as to remove the dry etching products thoroughly, the SiGe layer 3 becomes side etched, as shown in FIG. 2(b). This results from a high solubility the SiGe layer has for this mixed solution, and, in the case of the SiGe layer containing not less than 10 atomic % of Ge and especially not less than 20 atomic % of Ge, this problem of side etching of the SiGe layer becomes far more serious. Such a side etching of the SiGe layer within a gate electrode may bring about defective device operations.
In effect, with the conventional cleaning method wherein a mixed solution of ammonia and hydrogen peroxide is utilized as a cleaning solution for cleaning (a cleaning agent), it is highly difficult to achieve thorough removal of dry etching products and particles which are stuck on the semiconductor substrate, while preventing side etching of the SiGe layer. In addition, for attaining excellent device characteristics, it is essential not to damage the gate oxide film, either.
Accordingly, an object of the present invention is to manufacture, in a high yield, a semiconductor device having excellent device characteristics and good reliability by performing, by means of dry etching, patterning of a layered film which comprises a SiGe film containing Si and Ge and an oxide film to form a gate electrode pattern and a gate oxide film pattern, and thereafter removing thoroughly dry etching products and particles which are stuck onto the semiconductor substrate, without damaging the SiGe layer and the gate oxide film which constitute the gate.
The present invention provides a method of manufacturing a semiconductor device having, on a semiconductor substrate, a gate oxide film and a gate electrode which comprises a SiGe film containing Si and Ge which method comprises the steps of:
a patterning to form a gate electrode pattern as well as an oxide film pattern by applying dry etching to a layered film which is formed, on the semiconductor substrate, of an oxide film and the SiGe film, being laid in this order;
a first cleaning wherein, after the step of the patterning, the semiconductor substrate is cleaned with a first cleaning solution containing hydrofluoric acid; and
a second cleaning wherein, after the step of the first cleaning, the semiconductor substrate is cleaned with a second cleaning solution containing ammonia and hydrogen peroxide.
Further, the present invention provides a method of manufacturing a semiconductor device, wherein:
an ammonia concentration in the second cleaning solution is 0.05%-1.5 weight %; and
a content ratio (by weight) of hydrogen peroxide to ammonia in the second cleaning solution is not less than 1 (hydrogen peroxide/ammonia).
Further, the present invention provides a method of manufacturing a semiconductor device, wherein, in the step of the second cleaning, the temperature of the second cleaning solution in use is not higher than 45xc2x0 C.
Further, the present invention provides a method of manufacturing a semiconductor device, wherein a hydrogen fluoride concentration in the first cleaning solution is 0.05 weight %-1.0 weight %.
In the present invention, after a layered film wherein an oxide film and a SiGe film are laid in this order is patterned by means of dry etching and thereby a gate electrode pattern and a gate oxide film pattern are formed, cleaning to remove etching products and particles is carried out in two steps, that is, the step of first cleaning suited to remove etching products and the step of second cleaning suited to remove particles. As a result, in each cleaning step, the cleaning solution optimal to remove each of the contaminants therein can be used so that excellent cleaning effects can be obtained. Moreover, because each employed cleaning solution has a strong cleaning effect on its contaminants for the removal and besides the concentration and the composition of the cleaning solution as well as cleaning conditions can be chosen specifically for each cleaning step, the dissolving powers of the cleaning solution for the SiGe layer and the gate oxide film and, in other words, side etching to the SiGe layer and the gate oxide film can be well suppressed, while securing the cleaning effect on the contaminants for the removal satisfactorily.
In the present invention, an object of the step of first cleaning is to remove mainly dry etching products and, therein, the semiconductor substrate is cleaned with the first cleaning solution containing hydrofluoric acid. The present inventors recognized that hydrofluoric acid utilized as the first cleaning solution has a very strong removing power on dry etching products but not on particles. In general, hydrofluoric acid is known to have a strong removing power over oxides and, thus, its use as a cleaning agent in a state where the gate oxide film is exposed is thought to cause damage to the gate oxide film. However, it was found out that as a removing power of hydrofluoric acid on dry etching products is very strong, even if its removing power is somewhat weakened by lowering its concentration in the cleaning solution, dry etching products can be removed still satisfactorily. In effect, in the present invention, the use of hydrofluoric acid as the first cleaning solution makes it possible to remove dry etching products satisfactorily, while suppressing well the side etch of the gate oxide film. Furthermore, the first cleaning solution containing hydrofluoric acid has such a low etching rate for the SiGe layer that the side etch the SiGe layer in the step of first cleaning can be neglected.
In the present invention, an object of the step of second cleaning is to remove mainly particles and, therein, the semiconductor substrate is cleaned with the second cleaning solution made of a mixed solution of ammonia and hydrogen peroxide. The present inventors recognized that a mixed solution of ammonia and hydrogen peroxide utilized as the second cleaning solution has a very strong removing power on particles in a specific composition range but not on dry etching products. Although a mixed solution of ammonia and hydrogen peroxide is widely known as a cleaning agent, it has a very high etching rate of the SiGe layer at a conventionally employed concentration, and, thus, when used in the step of second cleaning, a considerable side etch of the SiGe layer may be brought about, though its removal of particles is satisfactory. However, the present inventors found out that as far as the content ratio of hydrogen peroxide to ammonia is confined within a specific range, even if its etching rate of the SiGe layer is far reduced by lowering the concentration of the cleaning solution, such a removing power on particles as required in the present invention can be still readily obtained. In effect, in the present invention, the use of a mixed solution of ammonia and hydrogen peroxide as the second cleaning solution makes it possible to remove particles satisfactorily, while suppressing well the side etch of the SiGe layer. Furthermore, the second cleaning solution made of a mixed solution of ammonia and hydrogen peroxide has such a low etching rate for the gate oxide film that the side etch of the gate oxide film in the step of second cleaning can be neglected.
As described above, in the present invention, after a layered film having, on a semiconductor substrate, an oxide film and a SiGe film in this order is patterned by dry etching and thereby a gate electrode pattern and a gate oxide film pattern are formed, the semiconductor substrate is cleaned in two steps, namely, in the step of first cleaning for removing mainly dry etching products and in the step of second cleaning for removing mainly particles, whereby dry etching products and particles which are stuck on the semiconductor substrate can be removed satisfactorily, while suppressing the side etching of the SiGe layer which constitutes the gate electrode as well as the gate oxide film. As a result, a semiconductor device with excellent device characteristics and good reliability may be manufactured with a high yield.